Gordonia sputi-associated bloodstream infection in a renal transplant patient with chronic indwelling central venous catheter: a case report and literature review

Introduction. Although rare, human infections caused by Gordonia spp. have been reported, especially within the immunocompromised population and those with long-term indwelling devices. We report a case of Gordonia spp. bacteraemia in a renal transplant patient and present a literature review on microbiological identification methods of this organism. Case Presentation. A 62-year-old female renal transplant recipient admitted to hospital with a 2-month history of dry cough and fevers occurring weekly when receiving electrolyte replacement infusions via a Groshong line. Over 2 weeks, blood cultures repeatedly isolated a Gram-positive bacillus solely in aerobic bottles, and this was initially reported as Rhodococcus spp. by the local microbiology laboratory. Chest computed tomography (CT) showed multiple ground-glass lung opacities suggestive of septic pulmonary emboli. As central line-associated bloodstream infection was suspected, empirical antibiotics were initiated and the Groshong line was removed. The Gram-positive bacillus was later confirmed by the reference laboratory as Gordonia sputi via 16S rRNA sequencing. Vancomycin and ciprofloxacin for a duration of 6 weeks were completed as targeted antimicrobial therapy. After treatment, the patient remained symptom-free with marked improvement on repeat CT chest imaging. Conclusion. This case illustrates the challenges surrounding identification of Gordonia spp. and other aerobic actinomycetes. 16S rRNA gene sequencing may be a preferred identification method, especially when initial workup of a weakly acid-fast organism fails to make an identification or shows discrepant results using traditional diagnostic modalities.


INTRODUCTION
Gordonia spp. are aerobic, Gram-positive, rod-shaped bacteria of the order Actinomycetales. They are ubiquitous in the environment and are regarded as opportunistic pathogens [1].
Although rare, reported infections range from mediastinitis post-sternotomy for cardiac surgery, pneumonia, brain abscesses and meningitis through to various skin and soft tissue infections [2]. Among immunocompromised patients with chronic indwelling catheters and medical devices, Gordonia spp. have also been implicated in cases of catheter-related bacteraemia [2].

ACCESS
Frequent misidentification of Gordonia spp. as other Gram-positive bacilli (e.g. Corynebacteria, Nocardia, Rhodococcus) may delay appropriate diagnosis and treatment, including the dismissal of positive blood cultures as contaminating diphtheroids [3][4][5]. We report here a case of central line-associated bloodstream infection (CLABSI) due to Gordonia sputi in a renal transplant recipient that was initially misidentified as Rhodococcus spp. by the analytic profile index (API) Coryne system (bioMérieux, Marcy L'Étoile, France). We performed a literature review of human infections caused by Gordonia spp., as well as reviewing the diagnostic modalities used to identify the organism and the challenges faced.

CASE PRESENTATION
A 62-year-old female renal transplant recipient was admitted to hospital on 20 August 2021, with a 5 week history of recurrent fevers and progressive dry cough without haemoptysis or dyspnoea. She did not report any unintentional weight loss, night sweats, fatigue or altered mentation. She had no recent sick contact exposures (including no prior risk of exposure to tuberculosis) or significant travel history. Her past medical history included deceased donor renal transplant in October 2012, stable on tacrolimus and mycophenolate mofetil without any history of rejection. Other medical and surgical history included workup for chronic hypophosphataemia and hypocalcaemia requiring weekly electrolyte replacement infusions via Groshong line (inserted March 2021), prior hemicolectomy for diverticular disease and parathyroidectomy.
On examination, she was haemodynamically stable with blood pressure of 151/67, pulse rate of 69 beats min −1 and body temperature of 36.8 °C. Lung auscultation was normal without any bilateral adventitious sounds, and cardiovascular examination did not reveal any murmurs or other stigmata of infective endocarditis. Groshong line site did not demonstrate purulent discharge or overlying cellulitis. Laboratory investigations showed a peripheral white blood cell count of 5.1×10 9 l −1 (normal range 4.5-11.0×10 9 l −1 ) with a neutrophil count of 3.4×10 9 l −1 (normal range 2.0-8.0 x 10 9 l −1 ). Inflammatory markers were elevated with C-reactive protein of 23.2 mg l −1 (normal <3.1 mg l −1 ).
Chest radiograph followed by whole-body computed tomography (CT) scan revealed multifocal ground-glass opacities suspicious for pulmonary septic emboli, without cavitary lesions (Fig. 1). Transthoracic and subsequent trans-oesophageal echocardiography were negative for vegetations or haemodynamically significant valvular dysfunction. In the context of recurrent fevers occurring in temporal relation to weekly electrolyte infusions, outpatient blood cultures were initially obtained 2 weeks prior to admission and Gram-positive bacilli were only isolated from the aerobic bottle. The patient was initiated on intravenous (IV) vancomycin. Questions remained as to whether the positive blood culture was attributable to contamination and initially the organism was not identified using MALDI-TOF VITEK MS V3 (bioMérieux, Marcy L'Étoile, France). Subsequent repeat blood cultures collected both from peripheral draw and tunnelled Groshong line over a 2 week period continued to isolate Gram-positive bacilli only in aerobic bottles (Figs 2 and 3). The organism showed beige, non-haemolytic colonies that were mucoid in appearance and adherent to media, catalase-positive and partially acid-fast. In our local microbiology laboratory, API Coryne system (bioMérieux, Marcy L'Étoile, France) gave an identification of Rhodococcus spp.  Inoculum was prepared from blood agar after incubating the isolate for 3-5 days at 35 °C (+/− 2 °C), with suspension made to 0.5 McFarland standard. The minimum inhibitory concentrations (MICs) were determined using E-test gradient strip (bioMérieux, France) as part of non-standardized susceptibility testing for this isolate. Findings were interpreted as per Clinical and Laboratory Standards Institute (CLSI) M24 [6]. The results showed susceptibility to amoxicillin/clavulanate, azithromycin, ciprofloxacin, linezolid, penicillin and vancomycin; it was intermediate to doxycycline. Hence, oral ciprofloxacin 500 mg twice daily was added to the patient's regimen on the third day of admission as combination antimicrobial therapy. As her Groshong line was the suspected source of bacteraemia, it was subsequently removed and the catheter tip bacterial culture isolated Gram-positive bacilli after 4 days of incubation. Repeat blood cultures after 5 days of antibiotics (1 day post-line removal) were negative.

DIAGNOSIS, TREATMENT AND FOLLOW-UP
As our local diagnostic methods failed to identify an organism matching with grown colony morphology and biochemical properties, the isolate was forwarded to the provincial reference laboratory for 16S rRNA sequencing, where the organism was subsequently identified as G. sputi.
Symptom association with Groshong catheter use, suspected septic pulmonary emboli and prompt resolution of bacteraemia following central venous catheter removal were consistent with a diagnosis of CLABSI. Six weeks of IV vancomycin plus oral ciprofloxacin post-line removal were given based on concerns for complicated bacteraemia in the setting of radiographical evidence of suspected pulmonary septic emboli and lack of standardized susceptibility results or treatment standards. The patient was clinically stable and thus discharged home to complete the course of antibiotics. By completion of antibiotics, her fever and dry cough had resolved, and a new Groshong line (placed 8 days post-clearance of blood cultures) was functioning well with no new signs of infection. Repeat CT chest post-treatment showed marked interval improvement of the multifocal ground-glass opacities with only minimal residual left upper lobe parenchymal scarring. The patient remained symptom-free 3 months post-completion of therapy.

DISCUSSION
Reported risk factors for Gordonia-associated infections include implanted catheters and medical devices, active chemotherapy treatment, haematological malignancies, receipt of solid organ or haematopoietic stem cell transplant, or recent surgery [e.g. coronary artery bypass graft (CABG)] [2,3,7,8]. Gram-positive bacilli isolated in blood cultures of patients with clinical suspicion of infection should not be routinely dismissed as contaminating diphtheroids, especially in patients who are immunocompromised or have long-term indwelling catheters or medical devices, or when isolated in multiple culture bottles [3][4][5].
The number of recognized infections due to Gordonia spp. may rise in the future because of the increased use of long-term indwelling central venous catheters and medical devices, extended survival of immunocompromised patients and improved laboratory identification methods. Early genus-or species-level identification of Gram-positive bacilli such as Gordonia spp. from cultures of individuals with suspected infections is key for early diagnosis and targeted therapy. However, challenges remain in the ability to identify these organisms accurately and reliably via traditional culture identification methods.
A comprehensive literature review was conducted on all English language articles published on human infections due to Gordonia spp. using EMBASE and Ovid MEDLINE from 1946 (inception) to February 2022 (File S1, available in the online version of this article). All cases of human infections with Gordonia spp. isolated in cultures, including from case report/series, observational studies, or clinical trials, were included. We excluded any duplicate data, non-English articles, non-human infections, review articles (without primary data) and reports from reference laboratory or public health reports (i.e. those that focused on evaluation and workup of non-clinical isolates). Our search identified 57 eligible articles, of which 92 documented human infections associated with Gordonia spp. were reported [1-5, 7-58] (see Table 1 for details).
The median age was 50 years (interquartile range 30-65 years) and 54.7 % of patients were male. Reported cases predominantly involved healthcare sites in Asia (38 %) and North America (37 %). Of reported clinical risk factors, 31.5 % of patients had central venous catheter or haemodialysis lines, and 20.7 % were receiving peritoneal dialysis. Approximately a quarter of patients were immunocompromised, including haematological malignancy with active chemotherapy (15.2 %), solid tumours with active chemotherapy (7.6 %) and solid organ or bone marrow transplant (5.4 %). Other risk factors included post-operative status from cardiac surgery (e.g. CABG) 9.0 % and diabetes mellitus (7.6 %).
For the preliminary identification modality (Table 2), the API Coryne system (bioMérieux, Marcy L'Étoile, France) was most frequently used (20 of 92 isolates; 21.7 %), but 17/20 (85.0 %) species were misidentified as Rhodococcus. MALDI-ToF VITEK MS (8 of 92 isolates, 8.7 %) showed more accurate performance, although 2 of the 8 isolates in that subgroup (25.0 %) failed to provide any identification. With MALDI-ToF VITEK MS, six of the eight isolates were successfully identified Gordonia spp., although 16S rRNA sequencing was required for all for species-level identification. PCR for the hsp65 gene (3.3 %, three isolates) also showed successful identification up to genus level prior to proceeding to 16S rRNA sequencing for species-level identification. Thirty of the 92 isolates (32.6 %) in our listed studies did not clearly report any diagnostic modality for preliminary identification. For definitive identification of Gordonia isolates, 16S rRNA sequencing was the most common reported modality, with 80/92 isolates (87.0 %).
Our clinical case and literature review highlight issues surrounding misidentification of Gordonia spp. using conventional methods of identifying modified acid-fast organisms. Based on our review, 16S rRNA sequencing is the preferred identification method.
As 16S rRNA sequencing may not be readily available and requires submission to a reference laboratory, consideration of prioritization of early 16S rRNA sequencing may include: isolates staining weakly acid-fast with discrepant or no initial identification, suspicious characteristics from morphology (e.g. non-motile short Gram-positive rods as opposed to coccobacillary, suggesting non-Rhodococcus spp.; absence of aerial hyphae suggesting a non-Nocardia spp.), or biochemical results (e.g. positive for urea hydrolysis and nitrate reduction; or unable to grow in the presence of lysozyme, also suggesting a non-Nocardia spp.).
There are currently no guidelines for the management of Gordonia infections [2] or established breakpoints per the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) for Gordonia spp. While dual empirical antimicrobial therapy may be considered (e.g. carbapenems, fluoroquinolones, vancomycin), treatment should be individualized and informed by the isolate's in vitro antimicrobial susceptibility test results and clinical response to treatment [3,39].
Our literature review showed successful treatment using various antimicrobials of varying durations, depending on the type and severity of infection. Recently, the in vitro antimicrobial susceptibilities of 13 human isolates of Gordonia polyisoprenivorans were reported, where nearly half of the strains were resistant to trimethoprim-sulfamethoxazole [59]. At least for G. polyisoprenivorans, some strains were resistant to tigecycline, minocycline and clarithromycin. All isolates were susceptible to amikacin, ampicillin, ceftriaxone, imipenem, amoxicillin-clavulanate, ciprofloxacin, vancomycin and linezolid [59]. With the absence of guidelines, treatment duration and the role of lifelong suppression in immunocompromised hosts or infections with non-removable hardware require further study. Treatment decisions should be based on the host's underlying immune function, specific immunosuppression and modifiability of infection risk factors.

Funding information
This work received no specific grant from any funding agency.

Peer review history
Thank you for your letter on March 1 st , 2023 regarding our submission to Access Microbiologyentitled, "Gordonia sputi -associated bloodstream infection in a renal transplant patient with chronic indwelling central venous catheter: a case report and literature review" (manuscript ID ACMI D-23-00005).
My colleagues and I greatly appreciate the opportunity to revise and improve our manuscript based on the thoughtful suggestions made by the two reviewers. We have implemented the feedback and clarified potential questions provided by them.
Furthermore, in our study's literature review, the majority of the case reports provided successful identification, including to species level. In order to improve readability for our audience, we also modified Table 2 to incorporate further details on the proportion of isolates that were correctly identified or initially misidentified in correspondence with the identification modality (see changes on Table 2).
Comment #4 - To clarify when discussing about 32.6% of isolates, we are referring to "preliminary identification of isolate". This would include any initial workup including use of MALDI-ToF VITEK MS for proteomic analysis, API Coryne (i.e., biochemical testing). Given some of the cases occurred in countries with limited diagnostic facilities on local basis (e.g., do not have MALDI-ToF mass spectrometry available), it is clinically sensible that they have sent those isolates to reference laboratory directly for 16s-sequencing or other advanced techniques to achieve identification.
Meanwhile, our quoted "80/92" or 87% of isolates with 16s sequencing is referring specifically to the definitive or final confirmatory identificationof Gordoniaisolates within our included studies. We have already emphasized this at the end of line 153-156 for our manuscript: where we mentioned 30/92 isolates did not clearly listed any diagnostic modality for preliminary identification. For definitive identification, 16s-rRNA sequencing was the most commonly reported modality.
Response #6: Thank you for identifying this typo mistake. It has been corrected with appropriate capitalization. (see Discussion, Line 163)